Controls of chromium and third element contents in nickel-base alloys for corrosion resistant alloys in hot HNO-HF mixtures

Takeuchi, Masayuki ; Nakajima, Yasuo  ; Hoshino, Kuniyoshi*; Kawamura, Fumio*

Corrosion resistance of nickel-base alloys in HNO-HF mixtures was investigated to apply them to FLUOREX process, which is advanced hybrid process of fluoride volatility and solvent extraction for next-generation spent nuclear oxide fuel reprocessing. Many types of Ni-Cr and Ni-Cr-X (X= Mo, W, Nb, Ti, Si, Cu) ingots were experimentally manufactured and the desirable chromium and third element contents in nickel-base alloys were discussed in narrow range to improve the corrosion resistance in hot HNO-HF mixtures. From the results of corrosion tests, Ni-45Cr-0.25Mo alloy exhibited the best corrosion resistance in this study. The corrosion rate was 0.17mm/y in 8M HNO-0.1M HF solutions at 373K and it provided good performance as corrosion resistant materials. In conclusion, it was found that the control of higher chromium content and a small amount of molybdenum in nickel-base alloys are significant to improve the corrosion resistance in HNO-HF mixtures.